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A. A. Natale

Publications and source records attributed to A. A. Natale.

At least 55 records · Page 3Linked to original sources
arXiv2009

Non-leptonic annihilation decays of B mesons with a natural infrared cutoff

Within the QCD factorization approach we compute the amplitudes for annihilation channels of B mesons decays into final states containing two pseudoscalar particles. These decays may be plagued by effects like non-perturbative physics or breaking of the factorization hypothesis and imply, at some extent, the introduction of an infrared cutoff in the calculation of amplitudes. We compute the decays with the help of infrared finite gluon propagators and coupling constants that were obtained in different solutions of the QCD Schwinger-Dyson equations. These solutions yield a natural cutoff for the amplitudes, and we argue that a systematic study of these B decays may provide a test for the QCD infrared behavior.

hep-ph↗
arXiv2008

Light composite Higgs from an effective action for technicolor

We compute an effective action for a composite Higgs boson formed by new fermions belonging to a general technicolor non-Abelian gauge theory, using a quite general expression for the fermionic self-energy that depends on a certain parameter (alpha), that defines the technicolor theory from the extreme walking behavior up to the one with a standard operator product expansion behavior. We discuss the values of the trilinear and quadrilinear scalar couplings. Our calculation spans all the possible physical possibilities for mass and couplings of the composite system. In the case of extreme walking technicolor theories we verify that it is possible to have a composite Higgs boson with a mass as light as the present experimental limit, contrary to the usual expectation of a heavy mass for the composite Higgs boson. In this case we obtain an upper limit for the Higgs boson mass, M_H ~ 700GeV for SU(2)_TC, and the experimental data on the Higgs boson mass constrain SU(N)_TC technicolor gauge groups to be smaller than SU(10)_TC.

hep-ph↗
arXiv2007

The small $x$ behavior of the gluon structure function from total cross sections

Within a QCD-based eikonal model with a dynamical infrared gluon mass scale we discuss how the small $x$ behavior of the gluon distribution function at moderate $Q^{2}$ is directly related to the rise of total hadronic cross sections. In this model the rise of total cross sections is driven by gluon-gluon semihard scattering processes, where the behavior of the small $x$ gluon distribution function exhibits the power law $xg(x,Q^2)= h(Q^2)x^{-ε}$. Assuming that the $Q^{2}$ scale is proportional to the dynamical gluon mass one, we show that the values of $h(Q^2)$ obtained in this model are compatible with an earlier result based on a specific nonperturbative Pomeron model. We discuss the implications of this picture for the behavior of input valence-like gluon distributions at low resolution scales.

hep-ph↗
arXiv2006

Phenomenology of infrared finite gluon propagator and coupling constant

We report on some recent solutions of the Dyson-Schwinger equations for the infrared behavior of the gluon propagator and coupling constant, discussing their differences and proposing that these different behaviors can be tested through hadronic phenomenology. We discuss which kind of phenomenological tests can be applied to the gluon propagator and coupling constant, how sensitive they are to the infrared region of momenta and what specific solution is preferred by the experimental data.

hep-ph↗
arXiv2006

$γp$ and $γγ$ scattering from $\bar{p}p$, $pp$ forward amplitudes in a QCD eikonal model with a dynamical gluon mass

We examine the $γp$ photoproduction and the hadronic $γγ$ total cross sections by means of a QCD eikonal model with a dynamical infrared mass scale. In this model, where the dynamical gluon mass is the natural regulator for the tree level gluon-gluon scattering, the $γp$ and $γγ$ total cross sections are derived from the $pp$ and $\bar{p}p$ forward scattering amplitudes assuming vector meson dominance and the additive quark model. We show that the validity of the cross section factorization relation $σ_{pp}/σ_{γp}=σ_{γp}/σ_{γγ}$ is fulfilled depending on the Monte Carlo model used to unfold the hadronic $γγ$ cross section data, and we discuss in detail the case of $σ(γγ\to hadrons)$ data with $W_{γγ} > 10$ GeV unfolded by the Monte Carlo generators PYTHIA and PHOJET. The data seems to favor a mild dependence with the energy of the probability ($P_{had}$) that the photon interacts as a hadron.

hep-ph↗
arXiv2005

Elastic scattering and the proton form factor

We compute the differential and the total cross sections for $pp$ scattering using the QCD pomeron model proposed by Landshoff and Nachtmann. This model is quite dependent on the experimental electromagnetic form factor, and it is not totally clear why this form factor gives good results even at moderate transferred momentum. We exchange the eletromagnetic form factor by the asymptotic QCD proton form factor determined by Brodsky and Lepage (BL) plus a prescription for its low energy behavior dictated by the existence of a dynamically generated gluon mass. We fit the data with this QCD inspired form factor and a value for the dynamical gluon mass consistent with the ones determined in the literature. Our results also provide a new determination of the proton wave function at the origin, which appears in the BL form factor.

hep-ph↗
arXiv2005

Strength of the Trilinear Higgs Boson Coupling in Technicolor Models

We discuss the strength of the trilinear Higgs boson coupling in technicolor (or composite) models in a model independent way. The coupling is determined as a function of a very general ansatz for the technicolor self-energy, and turns out to be equal or smaller than the one of the standard model Higgs boson depending on the dynamics of the theory. With this trilinear coupling we estimate the cross section for Higgs boson pair production at the LHC. This measurement is quite improbable in the case of a heavy standard model Higgs boson, but it will be even worse when this boson is dynamically generated.

hep-ph↗
arXiv2005

Influence of a dynamical gluon mass in the $pp$ and $\bar{p}p$ forward scattering

We compute the tree level cross section for gluon-gluon elastic scattering taking into account a dynamical gluon mass, and show that this mass scale is a natural regulator for this subprocess cross section. Using an eikonal approach in order to examine the relationship between this gluon-gluon scattering and the elastic $pp$ and $\bar{p}p$ channels, we found that the dynamical gluon mass is of the same order of magnitude as the {\it ad hoc} infrared mass scale $m_{0}$ underlying eikonalized QCD-inspired models. We argue that this correspondence is not an accidental result, and that this dynamical scale indeed represents the onset of non-perturbative contributions to the elastic hadron-hadron scattering. We apply the eikonal model with a dynamical infrared mass scale to obtain predictions for $σ_{tot}^{pp,\bar{p}p}$, $ρ^{pp,\bar{p}p}$, slope $B^{pp,\bar{p}p}$, and differential elastic scattering cross section $dσ^{\bar{p}p}/dt$ at Tevatron and CERN-LHC energies.

hep-ph↗
arXiv2005

A dynamical mechanism to explain the top-bottom quark mass hierarchy

We discuss the mass splitting between the the top and bottom quarks in a technicolor scenario. The model proposed here contains a left-right electroweak gauge group. An extended technicolor group and mirror fermions are introduced. The top-bottom quark mass splitting turns out to be intimately connected to the breaking of the left-right gauge symmetry. Weak isospin violation occurs within the experimental limits.

hep-ph↗
arXiv2005

A dynamical gluon mass solution in a coupled system of the Schwinger-Dyson equations

We study numerically the Schwinger-Dyson equations for the coupled system of gluon and ghost propagators in the Landau gauge and in the case of pure gauge QCD. We show that a dynamical mass for the gluon propagator arises as a solution while the ghost propagator develops an enhanced behavior in the infrared regime of QCD. Simple analytical expressions are proposed for the propagators, and the mass dependency on the $Λ_{QCD}$ scale and its perturbative scaling are studied. We discuss the implications of our results for the infrared behavior of the coupling constant, which, according to fits for the propagators infrared behavior, seems to indicate that $α_s (q^2) \to 0$ as $q^2 \to 0$.

hep-ph↗
arXiv2004

A dynamical gluon mass solution in Mandelstam's approximation

We discuss the pure gauge Schwinger-Dyson equation for the gluon propagator in the Landau gauge within an approximation proposed by Mandelstam many years ago. We show that a dynamical gluon mass arises as a solution. This solution is obtained numerically in the full range of momenta that we have considered without the introduction of any ansatz or asymptotic expression in the infrared region. The vertex function that we use follows a prescription formulated by Cornwall to determine the existence of a dynamical gluon mass in the light cone gauge. The renormalization procedure differs from the one proposed by Mandelstam and allows for the possibility of a dynamical gluon mass. Some of the properties of this solution, such as its dependence on $Λ_{QCD}$ and its perturbative scaling behavior are also discussed.

hep-ph↗
arXiv2004

The origin of the first and third generation fermion masses in a technicolor scenario

We argue that the masses of the first and third fermionic generations, which are respectively of the order of a few MeV up to a hundred GeV, are originated in a dynamical symmetry breaking mechanism leading to masses of the order $αμ$, where $α$ is a small coupling constant and $μ$, in the case of the first fermionic generation, is the scale of the dynamical quark mass ($\approx 250$ MeV). For the third fermion generation $μ$ is the value of the dynamical techniquark mass ($\approx 250$ GeV). We discuss how this possibility can be implemented in a technicolor scenario, and how the mass of the intermediate generation is generated.

hep-ph↗
arXiv2003

Ultra peripheral heavy ion collisions and the energy dependence of the nuclear radius

To estimate realistic cross sections in ultra peripheral heavy ion collisions we must remove effects of strong absorption. One method to eliminate these effects make use of a Glauber model calculation, where the nucleon-nucleon energy dependent cross sections at small impact parameter are suppressed. In another method we impose a geometrical cut on the minimal impact parameter of the nuclear collision ($b_{min} > R_1 + R_2$, where $R_i$ is the radius of ion "$i$"). In this last case the effect of a possible nuclear radius dependence with the energy has not been considered in detail up to now. Here we introduce this effect showing that for final states with small invariant mass the effect is negligible. However when the final state has a relatively large invariant mass, e.g. an intermediate mass Higgs boson, the cross section can decrease up to 50%.

nucl-th↗
arXiv2003

Limit on the fermion masses in technicolor models

Recently it has been pointed out that no limits can be put on the scale of fermion mass generation $(M)$ in technicolor models, because the relation between the fermion masses $(m_f)$ and $M$ depends on the dimensionality of the interaction responsible for generating the fermion mass. Depending on this dimensionality it may happens that $m_f$ does not depend on $M$ at all. We show that exactly in this case $m_f$ may reach its largest value, which is almost saturated by the top quark mass. We make few comments on the question of how large can be a dynamically generated fermion mass.

hep-ph↗
arXiv2003

Medium effects in the pion pole mechanism (photon photon --> pion-zero --> neutrino-R antineutrino-L (neutrino-L antineutrino-R)) of neutron star cooling

Nuclear medium effects in the neutrino cooling of neutron stars through the exotic reaction channel γγ--> π^0--> ν_R \bar{ν_L} (ν_L \bar{ν_R}) are incorporated. Throughout the paper we discuss different possibilities of right-handed neutrinos, massive left-handed neutrinos and standard massless left-handed neutrinos (reaction is then allowed only with medium modified vertices). It is demonstrated that multi-particle effects suppress the rate of this reaction channel by 6-7 orders of magnitude that does not allow to decrease existing experimental upper limit on the corresponding π^0ν\barν coupling. Other possibilities of the manifestation of the given reaction channel in differente physical situations, e.g. in the quark color superconducting cores of some neutron stars, are also discussed. We demonstrate that in the color-flavor-locked superconducting phase for temperatures T < (0.1-10) MeV (depending on the effective pion mass and the decay width) the process is feasibly the most efficient neutrino cooling process, although the absolute value of the reaction is rather small.

astro-ph↗
arXiv2003

Phenomenological tests for the freezing of the QCD running coupling constant

We discuss phenomenological tests for the frozen infrared behavior of the running coupling constant and gluon propagators found in some solutions of Schwinger-Dyson equations of the gluonic sector of QCD. We verify that several observables can be used in order to select the different expressions of alpha_s found in the literature. We test the effect of the nonperturbative coupling in the tau-lepton decay rate into nonstrange hadrons, in the rho vector meson helicity density matrix that are produced in the chi_{c2} --> rho rho decay, in the photon to pion transition form factor, and compute the cross sections for elastic proton-proton scattering and exclusive rho production in deep inelastic scattering. These quantities depend on the infrared behavior of the coupling constant at different levels, we discuss the reasons for this dependence and argue that the existent and future data can be used to test the approximations performed to solve the Schwinger-Dyson equations and they already seems to select one specific infrared behavior of the coupling.

hep-ph↗
arXiv2003

Relating a gluon mass scale to an infrared fixed point in pure gauge QCD

We show that in pure gauge QCD (or any pure non-Abelian gauge theory) the condition for the existence of a global minimum of energy with a gluon (gauge boson) mass scale also implies the existence of a fixed point of the $β$ function. We argue that the frozen value of the coupling constant found in some solutions of the Schwinger-Dyson equations of QCD can be related to this fixed point. We also discuss how the inclusion of fermions modifies this property.

hep-ph↗